Typical optical fibers include a core material and a cladding material, with each of the core and the cladding being fabricated from fused silica and having dissimilar refractive indices. A fiber can be formed by drawing a preform, which can be a large mass that includes the core and cladding materials arranged in a shape that can resemble a cross-section of the finished fiber. The preform can be drawn in a fiber drawing tower, such that the preform can be heated and stretched from one end to form the optical fiber. As an example, optical fibers can be implemented in fiber lasers, such as for use in directed energy (DE) laser weapons. A DE laser weapon system can, for example, require near diffraction-limited (DL) laser sources with high optical power (e.g., at least 100 kW). As an example, to achieve a high optical power without degradation of beam quality, multiple fiber lasers can be combined via spectral or coherent beam combining.